In the prior art, potentiometers typically include three terminals, two of the terminals are fixed, and the remaining terminal can be moved. The moving terminal of a potentiometer is often called the third terminal. The range of the electrical signal output from the third terminal of a potentiometer is controlled by the input electrical signal potentiometer. A potentiometer's input electrical signal is typically either a voltage difference or a current provided by a source.
In one embodiment of a prior art potentiometer, the potentiometer comprises a cylinder, uniformly wound with a single layer wire, the cylinder side is exposed, the top and bottom of the cylinder are each provided with a terminal, the input voltage to the potentiometer is provided across the top and bottom terminals. The third terminal of the potentiometer is a metal stylus, where the metal stylus can slide up and down along the cylinder surface, and the wire wound on the cylinder is in contact with the stylus. The metal stylus voltage depends on the metal stylus position as it slides along the cylinder. The length of the wire is proportional to the total resistance of the potentiometer and the wire diameter is inversely proportional to the resistance. This potentiometer is also often referred to as a ‘wire-wound rheostat’.
In another embodiment of a prior art potentiometer, the potentiometer comprises a flat film has two terminals and narrow conduction band pattern on the film plate. A third terminal of the potentiometer in direct electrical contact with the film flat, and voltage of the third terminal depends on the position of the third terminal depends on the electrical contact position on the thin film. This potentiometer can be used to detect linear motion and angular motion.
In practice, these two potentiometer implementation types have some disadvantages. The third terminal of the two potentiometer types must move along the resistive element within the potentiometer, while maintaining good electrical contact is maintained between the third terminal and the resistive element of the potentiometer. However, long term use is complicated by contact corrosion, physical wear and tear, and loose wires; such that a potentiometer using mechanical components for a third terminal will show degraded electrical performance over time. There is a need for a mechanical device that can measure mechanical motion with improved reliability over the common potentiometer. Unfortunately, the wear mechanism is unavoidable in these mechanical devices. Accordingly, there is a need for a non-contact potentiometer, where the non-contact potentiometer third terminal does not need to come in direct contact with the conductive element in order to determine the position of the slider.
In the prior art, non-contact potentiometers often include a magnetic sensor and a magnet instead of a third terminal, the magnetic sensor in these devices detects the relative movement and position of the magnet. The magnetic sensor used for prior art contactless potentiometers is often a Hall Effect, an anisotropic magnetoresistance (AMR), or a giant magnetoresistance (GMR) sensor. The magnetic sensor for non-contact potentiometers can also be an inductive coil magnetic sensor. Inductive coil magnetic sensors operate by sending and receiving electromagnetic signals at a given frequency in the presence of a movable soft ferromagnetic component, and then determining the position of the soft magnetic component through algorithms and calibration. This type of non-contact type potentiometer is also known as a linear variable differential transformer (LVDT). This type of non-contact potentiometer solves wear problems during prolonged use.
However, this type of prior art non-contact potentiometer has poor precision, high power consumption, high cost, and added complexity due to the need for a circuit to convert the analog sensor signal into a digital signal.